Abstract: Endothelial cells (ECs) were considered to play a main role in postnatal angiogenesis until CD34+ mononuclear cells were isolated from peripheral blood by Asahara et al in 1997, and these cells were named as putative endothelial progenitor cells (EPCs). EPCs are a group of stem cells with angiogenic function, and have no specific immunophenotype. Identification of EPCs is mainly based on their vasculogenic ability. It is widely recognized that EPCs originate either from bone marrow or peripheral vascular wall. The cells which can differentiate to immature endothelial cells in vitro are called endothelial colony forming cells (ECFCs). Signals release from ischemic tissues mobilize the EPCs from bone marrow and guide them to migrate and home to the ischemic sites. The active EPCs recruit more resident ECFCs and ECs to form neomicrovessels and then promote the tissues repair. More intensive studies on the nature of EPCs will contribute to the development of clinical therapeutic angiogenesis research and methods.